Nanoscience of `Self' 2.0: blocking CD47 recognition by phagocytes in blood & solid tumor clearance
Nanoparticle coatings of PEG or other polymers have been a standard approach for prolonging circulation in
order to maximize delivery to disease sites. However, particles always develop a corona of serum proteins
including IgG, IgM, etc. that signal `eat me' to macrophages in the spleen, liver, and even tumors. Specific
antibodies can also develop, including anti-PEG.
CD47 is a protein on all of our cells that signals `Self' to macrophages and overrides `eat me' factors on
the surface of our cells. We showed human-CD47 inhibits phagocytosis of IgG-coated particles and RBCs that
signal at a `phagocytic synapse' through SIRPa [Tsai & Discher J Cell Biol 2008]. `Self'-nanobeads show
delayed clearance from the circulation and improved delivery to tumor xenografts in NOD/SCID/¿ (NSG) mice
with a human-compatible SIRPa [Rodriguez Science 2013]. Blocking SIRPa with antibody also eliminated `Self'
signaling. Our first R01 allowed us – among other accomplishments – to improve gene delivery to the same
xenograft model with novel nano-characterized CD47-Lentivirus [Sosale Mol Ther-MCD 2016], and we
developed a safe and effective therapy with SIRPa-inhibited macrophages [Alvey Curr Biol 2017]. We propose
to advance the safety and efficacy of this eng'd macrophage approach using diverse nano approaches.
Phase-I clinical trials in cancer patients are already using anti-(humanCD47) for blockade because
CD47 is expressed on cancer cells as on all cells. Initial reports from the anti-(humanCD47) trials are showing
anemia but no efficacy. Our mouse models injected with anti-(mouseCD47) likewise show no efficacy against
cancer and show anemia as well as anti-RBC IgG – and so the model is appropriate for our new approach.
Our overall hypothesis is that CD47 opposes engulfment and thereby inhibits acquired immunity. Our
goal is to show an eng'd macrophage therapy can be injected systemically and prove safe (no autoimmune
anemia) and sufficiently effective that mice cured of tumors acquire immunity to further injection of cancer cells.
Diverse nano-tools will help test the hypothesis and achieve our goal, including nanoparticle tests of acquired
immunity, nanoparticle tracking of eng'd macrophages, and new nano-Self blockade approaches.